1. Field of the Invention
The present invention relates to a color adjusting method that optimizes color signals to improve the reproduction of color in an image, and an image processing device applying the method. More particularly, the invention relates to a color adjusting method using a color-space transformation-matrix.
2. Description of the Related Art
Generally, a color space of an image input system, such as an image capturing apparatus, is different from a color space of an image output system, such as a display and a printer. For example, perceived color of a reproduced image, when a captured image is displayed on a monitor, is generally different from that of an original subject. Further, the difference between the perceived colors also depends on the properties of each output device.
Accordingly, color signals based on the sRGB standard which is a standard for the image input devices and image output devices, are generally used at present. The image input device outputs color signals after transforming the obtained RGB signals to signals based on the sRGB standard. Thereby, precise color reproduction is performed as long as the image output devices are compatible with the sRGB standard. Namely, tints quite similar to the original object can be reproduced. A variety of methods for performing color adjustment are known in the art. For example, the reproduced color can be converted to the original color by adjusting the spectrum characteristics of an optical filter, provided in an imaging system, to the sRGB standard or by transforming the RGB signals electronically by a matrix transformation.
Conventionally, multiple linear regression analysis is used to improve the accuracy of color transformation methods that use a color space transformation matrix for electronic color adjustment. Multiple linear regression analysis optimizes the matrix elements of the color-space transformation-matrix by a statistical analysis which considers the relationship between the original color and the reproduced color as a cause and effect relationship. Namely, the matrix elements are obtained by optimizing these elements under the condition that the difference between the signal levels of the predicted reproduced colors, which is obtained by performing a provisional color space transformation matrix operation on the RGB signals from the imaging system, and the signal levels of the original colors, is below or equal to a permissible value. For example, a method that uses multiple linear regression analysis to provide a matrix that transforms RGB signals to XYZ signals of a different calorimetric system is disclosed in the Japanese unexamined patent publication (KOKAI) No. 10-164381.